The invention relates to a batter switch, especially for use in a hand-operated electric tool which has a DC motor energized by a storage battery. The switch includes a longitudinally displaceable trigger which acts on a switching contact of a contact system, control electronics for changing the speed of the DC motor, a power transistor having a sheet metal cooling member and serving for changing the motor speed a freewheeling diode for protecting the control electronics.
Battery switches for electric tools are known which are constructed such that the power transistor is located outside the housing.
The transistor is electrically connected via litz wires to the control electronics and the switching system in the interior of the housing. A heat sink is connected to the power transistor.
As a rule, a freewheeling diode is plugged or soldered onto the printed circuit board of the control electronics, which is ineffective in conducting its heat to the outside. A changeover switch for right-handed/left-handed rotation is mounted on the actual switch, it being necessary here to provide leads from the actual switch to the R/L switch.
If there is a brake in these switches, it is often realized by a plurality of parts, it being the case that a positive opening is not always ensured by a spring-loaded brake contact. These switches have the disadvantage that fixing the power transistor to the switch via litz wires entails an increased requirement for parts, and thus higher costs. Furthermore, automatic installation of the switch in appliances provided therefore is difficult (flexurally slack parts). In addition, the transistor has to be screwed onto a heat sink.
A freewheeling diode that is fastened to the printed circuit board produces disadvantages because it heats up the control electronics and cannot conduct the heat to the outside.
The connecting lines from the switch to the R/L switch cause additional expenditure of installation and further connecting points which lead to voltage drops.
It is the object of the invention to remove these disadvantages. In particular, the aim is to eliminate connection of the power transistor via litz wires, which also leads to a reduction in parts.
Furthermore, the freewheeling diode is not to influence the control electronics by the heat produced.
In particular, it is to be possible for the heat produced in the switch, as caused by the contact system, freewheeling diode and brake, to be effectively conducted outside to the heat sink. Furthermore, the R/L switch is to be integrated in the actual switch by means of an appropriate arrangement, so that a compact design is achieved which has few connecting points and thus low losses.
This object is achieved by the invention, according to which the switch has a switch housing; first switch terminals connectable to the DC motor; second switch terminals connectable to the storage battery; a movable electric switching contact having open and closed positions; a manually engageable trigger slidably supported in the housing and cooperating with the switching contact for moving the switching contact into one of its positions; an electrically and thermally conducting one-piece bearing plate supported by the switch housing and control electronics having a power transistor for changing the motor current to vary the speed of the DC motor. The power transistor is supported by the bearing plate and is electrically and heat-transmittingly connected therewith. There is further provided a free wheeling diode which protects the control electronics and which has diode terminals. One diode terminal is electrically and heat-transmittingly connected to the bearing plate. An electrically conducting contact bar is connected to the other diode terminal, to one of the first switch terminals and to one of the second switch terminals; and an electrically and thermally conducting connecting post mounts the power transistor on the bearing plate. The power transistor is electrically connected to one of the second switch terminals by the switching contact in the closed position thereof and the bearing plate is connected to one of the first switch terminal.